Inheritance, Variation And Evolution Flashcards
What is sexual reproduction?
Type of reproduction.
Involves the production of gametes by meiosis.
A gamete from each parent fuses to form a zygote.
Genetic information from each gamete is mixed so the resulting zygote is unique.
What are gamates?
Sex cells
Haploid
What is meiosis?
Form of cell division involved in the formation of gamates in reproductive organs
Chromosome number is halved
Involves two divisions
What must occur prior to meiosis?
Interphase - copies of genetic information are made during this process
What happens during the first stage of meiosis?
Chromosome pairs line up along the cell equator
The pair of chromosomes are separated and move to opposite poles of the cell
Chromosome number is halved
What happens during the second stage of meiosis?
Chromosomes line up along the cell equator.
The chromatids are separated and move to opposite poles of the cell.
Four unique haploid gametes are produced.
Why is meiosis important for sexual reproduction?
It increases genetic variation.
It ensures that the zygote formed at fertilisation is diploid.
Describe fertilisation and its resulting outcome
Gametes join together to restore the normal number of chromosomes and the new cell then divides by mitosis. As the embryo develops, cells differentiate.
What are the advantages of sexual reproduction?
It creates genetic variation in offspring
Natural selection can be speeded up by humans in selective breeding
What is asexual reproduction?
Type of reproduction.
Involves mitosis only.
Produces genetically identical offspring known as daughter cells.
Describe the advantages of asexual reproduction
Only one parent is required.
Lots of offspring can be produced in a short period of time
Requires less energy and time as do not need a mate.
What are the disadvantages of asexual reproduction?
No genetic variation reducing the probability of a species being able to adapt to environmental change
Describe the circumstances in which Malarial parasites reproduce sexually and asexually
Sexual reproduction in the mosquito. Asexual reproduction in the human host.
Describe the circumstances in which fungi reproduce sexually and asexually
Asexual reproduction by spores.
Sexual reproduction to give variation.
Describe the circumstances in which plants reproduce sexually and asexually
Sexual reproduction to produce seeds.
Asexual reproduction by runners or bulb division
What is DNA?
A double-stranded polymer of nucleotides, wound to form a double helix
The genetic material of the cell found in its nucleus
What is genome?
The entire genetic material of an organism
Why is understanding the human genome important?
● Searching for genes linked to different types of disease.
● Understanding and treating inherited disorders.
● Tracing human migration patterns from the past.
What is a chromosome?
a long continuous thread of DNA that carries genetic information in the form of genes
How many chromosomes do human body cells have?
46 chromosomes (23 pairs)
How many chromosomes do humans gametes have?
23 chromosomes
What is a gene?
A small section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
What are the monomers of DNA?
nucleotides
What are DNA nucleotides made of?
Common sugar
Phosphate group
One of four bases: A, T, C or G
What are the four bases found in nucleotide?
Adenine, Thymine, Cytosine and Guaunine
Describe how nucleotides interact to form a molecule of DNA
Sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand
Base connected to each sugar
Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds
Explain how a gene codes for a protein
A sequence of three bases in a gene forms a triplet
Each triplet codes for an amino acid
The order of amino acids determines the structure (i.e. how it will fold) and function of protein formed
Why is the ‘folding’ of amino acids important in proteins such as enzymes?
The folding of amino acids determines the shape of the active site which must be highly specific to the shape of its substrate.
What is protein synthesis?
The formation of the protein from a gene
What are the two stages of protein synthesis?
transcription and translation
What does transcription involve?
The formation of mRNA from a DNA template
Outline transcription
- DNA double helix unwinds
- RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand
- RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand
- mRNA formation complete. mRNA detaches and leaves the nucleus.
What does translation involve?
A ribosome joins amino acids in a specific order dictated by mRNA to form a protein.
outline translation
- mRNA attaches to a ribosome.
- Ribosome reads the mRNA bases in triplets. Each triplet codes
for one amino acid which is brought to the ribosome by a tRNA
molecule (carrier molecule). - A polypeptide chain is formed from the sequence of amino
acids which join together.
What is a mutation?
A random change in the base sequence of DNA which results mostly in no change to the protein code for, or genetic variation of the protein (slight alteration but appearances and function remains)
Mutations occur continuously
Describe the effect of gene mutation in coding DNA
If a mutation changes the amino acid sequence, protein structure and function may change (an enzyme may no longer fit its substrate binding site or a structural protein may lose its strength).
If a mutation does not change amino acid sequence, there is no effect on protein structure or function.
What is non-coding DNA?
DNA which does not code for a protein but instead controls gene expression
Describe the effect of gene mutation in non-coding DNA
Gene expression may be altered, affecting protein production and the resulting phenotype.
What are alleles?
different versions of the same gene
What is a dominant allele?
A version of a gene where only one copy is needed for it to be expressed
What is a recessive allele?
A version of a gene where two copies are needed for it to be expressed
What is meant when an organism is homozygous?
When an organism has two copies of the same allele (two recessive or two dominant).
What is meant when an organism is heterozygous?
When an organism has two different versions of the same gene (one dominant and one recessive).
What is the genotype?
The genes present for a trait
What is phenotype?
physical (visible) characteristics
How are dominant alleles represented in the punnet square?
They are represented using uppercase letters.
How are recessive alleles represented?
They use the lower case version of the same letter as the dominant allele
What is the problem with single gene crosses?
Most characteristics are controlled by multiple alleles rather than just one
What is an inherited disorder?
A disorder caused by the inheritance of certain alleles.
Give 2 examples of inherited disorders
● Polydactyly (having extra fingers or toes) - caused by a dominant allele.
● Cystic fibrosis (a disorder of cell membranes) - caused by a recessive allele.
How are embryos screened for inherited disorders?
During IVF, one cell is removed (from an 8 cell embryo) and tested for disorder-causing alleles. If the cell doesn’t have any indicator alleles, then the originating embryo is implanted into the uterus.
What are ethical issues concerning embryo screening?
It could lead to beliefs in society that being disabled or having a disorder is less human or associated with inferiority.
The destruction of embryos with inherited disorders is seen by some as murder as these would go on to become human beings.
It could be viewed as part of the concept of designer babies as it may be for the parents convenience or wishes rather than the child’s wellbeing.
What are the economic issues concerning embryos screening?
Cost of hospital treatment and medication will need to be considered if it is known that a child will have an inherited disorder and financial support explored I’d necessary
What are the social issues concerning embryos screening?
Social care for children with inherited disorders may need to be considered if parents are unable to provide care
If an embryo is found to have an inherited disorder and is terminated, this can prevent a child and its parents from potential suffering in the future due to the disorder
What is gene therapy?
The insertion of a normal allele into the cells of a person with an inherited disorder to functionally replace the faulty allele.
What are ethical concerning gene therapy?
Some people believe that it is going against and ‘playing God’.
The introduced genes could enter sex cells and so be passed to future generations.
What are sex chromosomes?
A pair of chromosomes that determine sex:
● Males have an X and a Y chromosome
● Females have two X chromosomes
Why does the inheritance of a Y chromosome mean that an embryo develops into a male?
Testes development in an embryo is stimulated by a gene present on the Y chromosome
What is a sex-linked characteristics?
A characteristic that is coded for by an allele found on a sex chromosome
Why are the majority of genes found on the X chromosome rather than the Y chromosome?
The X chromosome is bigger than the Y chromosome so more genes are carried on it.
why are men more likely to show sex-linked recessive traits than women?
Many genes are found on the X chromosome that have no counterpart on the Y chromosome
Women (XX) have two alleles for each sex-linked gene whereas men (XY) often have one allele, only one recessive allele is required to produce the recessive phenotype in males
What is variation?
Differences in the characteristics of individuals in a population
What is causes of variation within a species?
Genetics and environmental
What is genetic variation?
Variations in the genotypes of organisms of the same species due to the presence of different alleles
Creates differences in phenotypes
What creates genetic variation in a species?
Spontaneous mutations
Sexual reproduction
State the three types of gene mutation
insertion, deletion, substitution
How may a gene mutation affect an organism’s phenotype?
Neutral mutation does not change the sequence of amino acids. Protein structure and function same. No effect on phenotype.
Mutation may cause a minor change in an organism’s phenotype e.g. change in eye colour.
Mutation may completely change the sequence of amino acids. This may result in a non-functional protein. Severe changes to phenotype.
What is the consequence of a new phenotype caused by a mutation being suited to an environmental change?
There will be a rapid change in the species.
What is evolution?
The gradual change in the inherited characteristics of a population over time (occurs due to natural selection which may result in the function of a new species)
Outline the theory of natural selection
All species of living things have evolved from simple life forms that first developed more than 3 billion years ago.
1. Genetic variation exists due to spontaneous mutations.
2. Selection pressures (e.g. competition, disease) exist.
3. Random mutation gives an organism a selective advantage.
4. Organism is better adapted to the environment and survives.
5. Organism reproduces, passing on its beneficial alleles.
6. Frequency of advantageous alleles increase.
How do two populations become different species?
When their phenotypes become different to the extent that they can no longer interbreed to produce fertile offspring.
What is selective breeding?
The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes
Outline the main steps involved in selective breeding
- Identify a desired characteristic e.g. disease resistance
- Select parent organisms that show the desired traits and breed them together
- Select offspring with the desired traits and breed them together
- Process repeated until all offspring have the desired traits
Give examples of characteristics selected for in selective breeding
Disease resistance in crops
Higher milk or meat production in animals
Gentle nature in domestic dogs
Large flowers
What is the main advantage of selective breeding?
Creates organisms with desirable features:
● Crops produce a higher yield of grain
● Cows produce a greater supply of milk
● Plants produce larger fruit
● Domesticated animals
Other than in agriculture, where else is selective breeding useful?
In medical research
In sports e.g. horse racing
Outline the disadvantages of selective breeding
Reduction in the gene pool which becomes especially harmful if sudden environmental change occurs
Inbreeding results in genetic disorders.
Development of other physical problems
Potential to unknowingly select harmful recessive alleles.
What is genetic engineering?
The modification of the genome of an organism by the insertion of a desired gene from another organism - genes from chromosomes of humans and other organisms can be ‘cut out’ and transferred to cells of other organisms.
Give an example of uses for genetically modified plants
Disease resistance
Produce larger fruits
What is the use for genetically modified bacteria cells?
To produce human insulin to treat diabetes mellitus.
Describe the benefits of genetic engineering
Increased crop yields for growing population
Useful in medicine
GM crops produce scarce resources
Describe the risks of genetic engineering
- Long-term effects of consumption of GM crops unknown
- Negative environmental impacts
- Late-onset health problems in GM animals
- GM seeds are expensive. LEDCs may be unable to afford them or may become dependent on businesses that sell them.
What is the name for crops that have had their genetic modified?
Genetically modified (GM) crops
What is Bacillus thuringiensis?
A microbial sprayable bacterial spore that paraylzes the gut causing death.
How is genetic engineering used to protect crops against insects?
The gene for toxin production in Bt can be isolated and inserted into the DNA of crops.
Bt crops now secrete the toxin which kills any insect larvae that feed on it.
What are the benefits of Bt crops?
Increased crop yields (fewer crops damaged).
Lessens the need for artificial insecticides.
Bt toxin is specific to certain insect larvae so is not harmful to other organisms that ingest it.
What are the risks of Bt crops?
Long term effects of consumption of Bt crops unknown.
Insect larvae may become resistant to the Bt toxin.
Killing insect larvae reduces biodiversity.
Describe the process of genetic engineering
- DNA is cut at specific base sequences by restriction enzymes to create sticky ends.
- Vector DNA cut using the same restriction enzymes to create complementary sticky ends.
- Ligase enzymes join the sticky ends of the DNA and vector DNA forming recombinant DNA.
- Recombinant DNA mixed with and taken up by target cells
What is a vector?
A structure that delivers the desired gene into the recipient cell
How can plants be cloned?
Taking plant cuttings
Tissue culture
What is tissue culture?
Using small groups of cells from part of a plant to grow identical new plants.
Describe how plants are grown using tissue culture?
- Select a plant that shows desired characteristics
- Cut multiple small sample pieces from meristem tissue
- Grow in a petri dish containing growth medium
- Transfer to compost for further growth
What must be ensured when preparing tissue cultures?
Ensure aseptic conditions to prevent contamination by microorganisms
What does the growth medium contain?
Nutrients and growth hormones
What are the advantages of growing plants by tissue culture?
Fast and simple process.
Requires little space.
Enables the growth of many plant clones with the same desirable characteristics.
Useful in the preservation of endangered plant species
What are the disadvantages of growing plants by tissue culture?
- Reduction in the gene pool
- Plant clones often have a low survival rate
- Could unknowingly increase the presence of harmful recessive alleles
Describe the plant cutting method of plant cloning
Older but simpler method than tissue culture
Gardeners use this method to produce many identical new plants from a parent cell
Detail the process of the plant cuttings method of plant cloning
- A branch is cut off from the parent plant.
- The lower leaves of the branch are removed and the stem is
planted. - Plant hormones are used to encourage new root development.
- A plastic bag is used to cover the new plant to keep it warm and
moist. - New roots and a new plant is formed after a few weeks.
What does embryo transplanting involve?
Pre-specialised cells from a developing animal embryo are split apart.
The resulting separate but identical embryos are transplanted into host mothers.
Describe how adult cell cloning is performed
- The nucleus is removed from an unfertilised egg cell.
- The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell.
- An electric shock stimulates the nucleated egg cell to divide and it forms an embryo.
- The embryo cells contain the same genetic information as the adult body cell.
- When the embryo is a ball of cells, it is inserted into the uterus of an adult female to continue de
Outline the theory of evolution by natural selection
Individuals of a species show a wide range of variation for a characteristic. Those with the characteristic most suited to the environment will survive breed most successfully. The desirable characteristic that has enabled the individuals to survive are passed onto their offspring.
Why was Darwin’s theory of evolution not accepted initially?
Most people believed in creationism
Insufficient evidence to prove the theory
The mechanism of variation and inheritance was not known at that time
